1. Field of the Invention
The present invention relates to subsea pipelines and connectors and/or fittings used in the pipelines. More particularly, the invention relates to a ball joint used for connecting misaligned pipes in subsea pipelines.
2. Description of Related Art
Misalignment ball joints have been used in pipelines (e.g., subsea pipelines) for decades. Misalignment ball joint use increased dramatically in the 1960's due to a tremendous increase in the number of subsea pipeline tie-ins being used. Misalignment ball joints provide a great degree of tie-in flexibility and allow tie-in connections to be made even with limited diver visibility and/or with difficult or limited manipulation available due to rigid pipes.
Typical misalignment ball joints have an internal profile of the ball portion of the misalignment ball joint assembly that contains a conical funnel. The conical funnel accommodates misalignment of the ball joint in any plane (typically up to as great as 15° of misalignment). In some cases, at full misalignment (for example, about 15° of misalignment), the projection of the bore of the ball produces an apparent obstruction from the exposed spherical surface of the cup.
U.S. Pat. No. 4,045,054 to Arnold (“Arnold”), which is incorporated by reference as if fully set forth herein, used a guide sleeve to overcome problems associated with the apparent obstruction. The guide sleeve concept disclosed by Arnold, however, saw little to no use in the industry. The lack of use of any form of the guide sleeve in misalignment ball joints may have been likely due to the relative low sophistication of pigs during the era of Arnold. In addition, pigging studies from the United States and the United Kingdom indicated that no restriction in articulation was required for pig passage from the cup sphere toward the funnel and that by limiting the articulation of the ball joint to 5°, the cup sphere exposure did not detrimentally impinge on the pig.
In recent years, however, “intelligent” pigs have started gaining use in offshore pipeline inspection and all new pipelines are being reviewed for intelligent pig suitability. These intelligent pigs include, for example, fingers, shoes, wheels, and/or other similar components mounted on relatively fragile, spring-loaded suspension arms to keep sensors in contact with the pipe bore. Thus, these intelligent pigs may require a relatively smooth surface for passage through the misalignment ball joint. Any obstruction (such as the apparent obstruction produced by projection of the bore of the ball) may inhibit passage of an intelligent pig through the misalignment ball joint. The guide sleeve disclosed by Arnold removes the apparent obstruction.
Arnold discloses a sleeve that is truncated to provide clearance between the end of the sleeve and the ball conical funnel as the ball joint components are articulated relative to each other when the pipe bores of the two attached pipes are misaligned during installation and makeup. As the assembly articulates, however, an opening between the sleeve end and ball funnel is exposed in the plane of the articulation. The opening is sufficiently large to allow some sensors to engage the opening and the end of the sleeve, which may result in damage to the pig and subsequent inspection data loss.
Thus, there is a need for a misalignment ball joint that provides a relatively smooth surface to inhibit damage to the sensors of an intelligent pig. The relatively smooth surface may have little to no gaps along the surface for passage of an intelligent pig through the misalignment ball joint.